Summary of Work: The objective of this project is to develop quantitative descriptions of the uptake, distribution, and elimination of inhaled compounds in laboratory animals. This project includes both the development of physiologically based pharmacokinetic (pbpk) models of inhalation exposure, and the development of experimental methods to measure the physiological response to exposures. Inhaled xenobiotics often affect the ventilation mechanics of test animals. Physiological modeling and dosimetry depend heavily on the estimate of the rate of alveolar ventilation. An unrestrained whole body plethysmograph system (Buxco Electronics Inc.) has been set up as a resource for research studies performed in the inhalation facility and for other laboratories in the NIEHS. Operational procedures have been developed and studies conducted using this system to measure ventilation and airway resistance parameters in mice and rats immunized with ovalbumin then exposed to ovalbumin aerosol and challenged by an aerosol exposure to methachloine.